Bessel Beam Generation Device and Optical Scanning Device Using Same

The present invention relates to, for example, a Bessel beam generating device having a large depth of focus, and an optical scanning device using the same.

Conventionally, an OCT (Optical Coherence Tomography) apparatus that generates a Bessel beam using an axicon lens is known (see, for example, Patent Document 1).

PTL1: Japanese Patent No. 5680776

However, in an OCT apparatus of such a configuration, because an axicon lens is used, the focal length from the axicon lens to the focus is restrictively short, requiring the distance to the object being irradiated to be set short. This imposes limitations on the design.

The present invention has been made to solve the above problem, and an object of the invention is to provide a Bessel beam generating device and an optical scanning device using the same that can improve design freedom (design flexibility).

To achieve the above object, a Bessel beam generating device according to the present invention is characterized by comprising: a group of at least four light emitters arranged at equal intervals on the same circle such that light is emitted from the tip of an optical waveguide portion, with the optical axis of the light emitted from each said light emitter maintained at the same angle with respect to the diameter direction of the circle; an entrance portion that splits a laser beam emitted from a single light source and causes the split beams to enter each of the optical waveguide portions; and an optical waveguide portion having a function to make the phase and amplitude of the emitted light from each said light emitter identical.

Further, an optical scanning device according to the present invention is characterized by comprising: a group of at least four light emitters arranged at equal intervals on the same circle such that light is emitted from the tip of an optical waveguide portion, with the optical axis of the light emitted from each said light emitter maintained at the same angle with respect to the diameter direction of the circle; an entrance portion that splits a laser beam emitted from a single light source and causes the split beams to enter each of the optical waveguide portions; an optical waveguide portion having a function to make the phase and amplitude of the emitted light from each said light emitter identical; a light receiving unit that receives return light of the emitted light (reflected from the measurement object) and converts it into an electrical signal; and an analysis unit that calculates the position of a reflection point of the measurement object by analyzing the electrical signal.

Furthermore, a Bessel beam generating device according to the present invention is characterized by comprising: a rotationally symmetric conical reflector whose generatrix is linear or curved with respect to the optical axis such that an incident laser beam is reflected outward relative to the optical axis; and a reflective cover portion arranged to cover the conical reflector, which re-reflects the wave reflected by the conical reflector using an elliptical surface main mirror having the optical axis as its axis of rotational symmetry.

An optical scanning device according to the present invention is characterized by comprising: a light source that emits a laser beam; a reflective lens on which the laser beam from the light source is incident and which reflects the laser beam outward from the optical axis; a reflective cover portion arranged to cover the reflective lens and that reflects the laser beam traveling outward toward the inside, thereby projecting a disk-shaped illumination beam; a light receiving unit that receives return light from the disk illumination beam and converts it into an electrical signal; and an analysis unit that calculates the position of a reflection point of the measurement object by analyzing the electrical signal.

According to the present invention, it is possible to realize a Bessel beam generating device and an optical scanning device using the same that can improve design flexibility.

Next, embodiments for carrying out the present invention will be described with reference to the drawings.

1 FIG. 2 FIG. 10 10 15 15 15 In, reference numeralindicates a disk-shaped Bessel beam generating device. In the disk-shaped Bessel beam generating device, as shown in, split beams divided from one light source are made to enter an optical fiberin which fiber tipA are arranged on the same circumference. The fiber tipA emit, as a disk-shaped Bessel beam, an irradiation beam having a donut-shaped cross-section with its central portion missing (i.e., a hollow center).

15 Here, a case will be described in which a single light source is split into 32 beams that are injected into 32 optical fiber, but the number of split beams is not limited. In order to generate a uniform disk-shaped Bessel beam, it is preferable to use 8 fibers, or more preferably 16 or more fibers.

A light source (not shown) that emits a laser beam is a laser light source for emitting laser light. There is no particular limitation on the wavelength of the laser light, and it is appropriately selected according to the object to be irradiated. For example, if the object to be irradiated is a human body, near-infrared light (780 nm to 2500 nm) is preferably used.

14 15 An entrance portionis provided to adjust the beam diameter of the split beams and efficiently couple them into the optical fiber. For example, coupling lenses, spherical lenses, rod lenses, or the like are used singly or in appropriate combination.

15 15 15 2 FIG. The optical fiberemits the split beam from its tip, which is the fiber tipA. Here, as shown in, the fiber tipA are arranged at equal intervals on a circle (indicated by a dashed line).

3 FIG. 3 FIG. 15 15 15 15 15 As shown in, the split beams incident into the optical fiberbecome diverging light with a divergence angle θ determined by the refractive index of the optical fiber, and are emitted from the fiber tipA as an irradiation beam. In, the fiber tipA is arranged perpendicular to the diameter of the circle; however, for example, it may be arranged tilted inward (tilted at an angle greater than 90° with respect to the diameter of the circle). This tilt angle (the angle between the diameter direction of the circle, as viewed from inside the circle, and the optical fiber) is set to be the same for all 32 optical fiber.

4 FIG. 16 15 16 As shown in, a lensis attached to the front end of the fiber tipA. The lensadjusts the traveling direction and divergence angle of the irradiation beam. Specifically, the divergence angle in the diameter direction of the circle is adjusted according to the desired depth of focus: when a greater depth of focus is desired, the divergence angle is made larger; when a smaller depth of focus is desired, the divergence angle is made smaller. The traveling direction of each irradiation beam is set according to the focal length: when the focal length is small, the tilt angle with respect to the diameter direction of the circle is small, and when the focal length is large, the tilt angle with respect to the diameter direction of the circle is large.

16 15 In the lens, the divergence angle of the irradiation beam is adjusted by the shape of the entrance surface and/or exit surface (or a combination of both). For example, if it is desired to increase the NA (Numerical Aperture) of the light beam emitted from the optical fiber, a convex lens with a bulging exit surface is suitably used; if it is desired to decrease the NA, a concave lens with a recessed exit surface is suitably used.

16 16 The lenscan also adjust the polarization direction of the irradiation beam as needed. Note that the lensmay be a single lens or a combination of two or more lenses. Here, since the same divergence angle and tilt angle are set for all the irradiation beams, the 32 irradiation beams overlap and combine while diverging and travel toward the center of the circle (travel perpendicular to the circumference), forming one donut-shaped disk illumination beam.

15 5 FIG. Since split beams with identical optical path lengths from a single light source are incident into the optical fiber, the disk illumination beam is focused so that its focal points coincide on the central axis, as shown in. At this time, because a focal point (indicated by a bold line) is formed on the central axis of the diverging disk illumination beam according to the overlap of the beams, it is possible to increase the depth of focus.

15 21 15 15 It is also possible to provide, just before the tip of the optical fiber, a voltage applying unitthat applies a voltage. By applying a voltage, the wavelength of the portion to which the voltage is applied can be temporarily changed, allowing the wavefront of the light to be advanced or delayed. Specifically, voltage is applied to half of the optical fibersuch that the optical fiberpositioned in the direction toward which the focal point is to be shifted has the highest voltage, and the voltage gradually decreases for fibers further away.

6 FIG. 14 1 14 17 14 9 In, by delaying the wavefront on the right side in the X-direction (indicated as X(R) in the figure), the focal position has shifted toward the right side of the page. In other words, to shift the focal position to the right side in the X-direction, voltages are applied to the fibers on the right side in the X-direction (A-toA-). Specifically, the highest voltage is applied to the fiberA-at the extreme right, and the voltage applied is gradually reduced for fibers toward the left.

7 FIG. 8 FIG. 22 22 16 16 15 As shown in, it is also possible to provide a lens driving unit. As shown in, the lens driving unitdisplaces the lensso as to change the angle at which the lensis incident relative to the fiber tipA. This allows the focal position in the Z-direction (the propagation direction of the disk illumination beam) to be shifted (moved along the optical axis of the disk illumination beam).

10 Next, the configuration when the disk-shaped Bessel beam generating deviceis used as an OCT (Optical Coherence Tomography) apparatus (an example of an optical scanning device) will be described.

9 FIG. 1 2 4 36 36 36 As shown in, an OCT apparatusincludes an external deviceand a measurement unitconnected by a line. There is no particular limitation on the line, and any known wired line capable of telecommunication can be used. Alternatively, a wireless network may be used in place of the line.

2 31 2 The external deviceis provided with a control unitcomposed of an MPU (Micro Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), etc., which integrally controls the entirety of the external device.

31 33 4 33 4 The control unitcontrols a display unitand the measurement unitaccording to user operation input, and displays on the display unitthe measurement results obtained by the measurement unit.

32 31 4 34 36 Specifically, when an operation input unitsupplies a request signal to start measurement, the control unitstarts a measurement process and supplies a start signal to the measurement unitvia an external interface(displayed as “External I/F” in the figure) and the line.

4 35 4 4 The measurement unitincludes a housingwith its bottom side exposed, and the measurement unitis housed inside. The start signal is supplied to the measurement unit.

10 FIG. 4 19 4 As shown in, the measurement unitis provided with a control unitcomposed of an MPU, ROM, and RAM, which integrally controls the entirety of the measurement unit.

19 11 11 11 11 41 When the start signal is supplied, the control unitcauses a light source (not shown) in a light generation unitto emit a laser beam. The light generation unitconverts the continuous laser beam emitted from the light source into a pulse beam with frequency modulation using an optical comb, and emits it. At this time, the light generation unitmay also perform phase modulation or frequency conversion as needed. Although not shown, the light generation unitsupplies to a signal processing unita detection signal based on a reference light beam whose optical path length has been adjusted such that it is approximately the same as (within the focal range of) the optical path length of the return beam from the measurement target.

11 12 13 13 13 The laser beam emitted from the light generation unitis converted into parallel light by a collimation unit, and then enters a beam splitting unit. The beam splitting unitsplits the parallel light into 32 split beams with identical optical path lengths. The beam splitting unitmay consist of an optical waveguide on a silicon or quartz substrate enabling optical wiring (such as an arrayed-waveguide grating (AWG)), or a combination of multiple optical elements ( for example, a combination of multiple beam splitters and multiple couplers (isolators), etc., with appropriate use of optical path length adjustment reflectors such as mirrors).

10 17 17 17 17 17 17 16 The split beams are directed into the disk-shaped Bessel beam generating devicevia an optical branching unit. Note that a separate optical branching unitmay be provided corresponding to each of the 32 split beams, or one optical branching unit may correspond to multiple split beams, or a single optical branching unitmay handle all split beams. For the optical branching unit, an optical element may be used that allows one of the outgoing light beam and the returning light beam to pass straight and bends the other beam (for example, a half-mirror type non-polarizing beam splitter, a polarizing beam splitter, an isolator, etc.) If a polarizing beam splitter is used as the optical branching unit, a quarter-wave plate is placed between the optical branching unitand the lens.

10 The disk-shaped Bessel beam generating deviceirradiates the measurement target with a disk-shaped Bessel beam as a disk illumination beam.

10 17 17 18 The disk-shaped Bessel beam generating devicealso directs the return light beam from the measurement target back into the optical branching unit. The optical branching unitdirects the return light beam into a light receiving unit.

18 41 41 11 41 19 The light receiving unitgenerates a measurement signal, which is an electrical signal corresponding to the received reference light beam and return light beam, and supplies it to a signal processing unit. The signal processing unitis also supplied with a reference signal generated from the optical comb in the light generation unit. This reference signal is supplied in synchronization with the timing of the electrical signal generated from the return light beam from the measurement target. The signal processing unitgenerates a measurement composite signal by combining the measurement signal and the reference signal, and supplies it to the control unit.

19 2 23 31 2 36 34 33 The control unitsupplies the measurement composite signal to the external devicevia the external interface. When the control unitof the external devicereceives the measurement composite signal via the lineand the external interface, it analyzes the measurement composite signal to calculate the positions of reflection points in the measurement target, generates image data, and displays it on the display unit.

11 12 FIGS.and 11 FIG. Next, a second embodiment will be described with reference to. The method of forming the irradiation beam differs from that of the first embodiment described above. Inand subsequent figures, components corresponding to those in the first embodiment are assigned reference numerals obtained by adding 100, and descriptions of the same components are omitted for brevity.

11 FIG. 110 110 In, reference numeralindicates a disk-shaped Bessel beam generating device. In the disk-shaped Bessel beam generating device, after a laser beam incident as diverging light is reflected outward, it is reflected from outside to inside, so that an irradiation beam having a donut-shaped cross-section is emitted.

115 116 115 116 An entrance portionemits a laser beam and directs it into a lens. The entrance portionmay be, for example, a light source, an optical fiber, or another optical component; in general it denotes the component or element positioned upstream of the lens.

116 126 126 116 126 The lensadjusts the divergence angle of the laser beam and directs the laser beam into an adjacent reflective cover portion. The reflective cover portionhas a shape, for example, of a part cut out from a spherical or ellipsoidal surface, and a reflective coating is formed on its entire surface except the area where it contacts the lens. Hereinafter, when laser light is incident on the reflective cover portion, the propagation direction of the optical axis at that time is called the forward direction Z_P of the laser light, and the backward direction is called the return direction Z_B.

126 125 125 125 The reflective cover portionhas an inner surface shaped as a portion of a sphere, ellipsoid, or parabolic surface (a high-order function curved surface). It transmits the incident laser light without alteration and directs it onto the reflective lens. The reflective lenshas a pointed shape, with a circular cross-section in the XY plane (for example, a conical shape). A reflective coating is formed on the side of the reflective lenson which the laser light is incident.

125 126 The reflective lensreflects the incident laser light outward (preferably at an angle of 80° to 170° relative to the forward direction Z_P of the laser light). The reflective cover portionreflects the laser light inward.

125 126 125 125 Here, by the outward reflection by the reflective lensand the inward reflection by the reflective cover portion, the laser beam becomes an irradiation beam directed inward. At this time, light that was near the optical axis before incidence on the reflective lensbecomes the outer portion after reflection, and light that was at the outer portion before incidence on the reflective lensbecomes the inner portion after reflection.

Therefore, low-intensity light overlaps at a nearer position, and high-intensity light overlaps at a farther position to form a focal point. This makes it possible to compensate for attenuation before the focal point by the intensity distribution of the laser light.

116 115 Note that by mounting the lensso that it can be tilted relative to the entrance portion(i.e., making it rotatable), it is also possible to adjust the irradiation direction of the disk illumination beam.

110 Next, the configuration when the disk-shaped Bessel beam generating deviceis used as an OCT (Optical Coherence Tomography) apparatus (optical scanning device) will be described.

12 FIG. 101 102 115 110 110 115 As shown in, an OCT apparatusincludes an external device, an entrance portionwhich is an optical fiber, and the disk-shaped Bessel beam generating device. The disk-shaped Bessel beam generating deviceis attached to the tip of the entrance portion(optical fiber).

102 131 102 The external deviceis provided with a control unitcomposed of an MPU, ROM, and RAM, which integrally controls the entirety of the external device.

132 133 102 4 111 117 114 118 119 In addition to an operation input unitand a display unit, the external deviceincludes, as compared to the first embodiment where those components were in the measurement unit, a light generation unit, an optical branching unit, an entrance portion, a light receiving unit, and a signal processing unit.

101 110 104 Thus, in the OCT apparatususing the disk-shaped Bessel beam generating device, because the number of components is small, the tip portion (measurement device) can be miniaturized (for example, to about a 1 mm square). This makes it suitable for applications such as catheters for imaging the interior of blood vessels.

111 118 118 119 The light generation unitsplits a pulse beam modulated by an optical comb and, after adjusting optical path lengths, supplies it as a reference light beam to the light receiving unit. The light receiving unitreceives the return light beam and the reference light beam, and supplies them as a measurement signal and a reference signal, respectively, to the signal processing unit.

The features of the groups of inventions extracted from the above embodiments will be described below, with the problems and effects as needed. Note that for ease of understanding, in the following description, the corresponding components in the above embodiments are appropriately indicated in parentheses or the like, but the invention is not limited to the specific configurations indicated in such parentheses. In addition, the meanings, examples, etc. of terms described in each feature may also be applied as meanings or examples of terms described in other features that use the same wording.

10 15 32 15 15 a group of optical fibers (optical fiber) comprising at least four optical fibers or more (optical fiber) is arranged such that their tips (fiber tipA) are on the same circle at equal intervals, and each said fiber tip is arranged such that it is tilted at the same angle with respect to the diameter direction of the circle; 14 an entrance portion (entrance portion) is provided that causes split beams obtained by splitting a laser beam from a single light source to enter each of the optical fibers; and 16 a lens (lens) is provided which adjusts the beam of light emitted from each said optical fiber so that diverging light with a donut-shaped cross-section having a hollow center that travels inward (toward the circle's center) is emitted as a disk illumination beam from the group of optical fibers. According to the above configuration, in the Bessel beam generating device (disk-shaped Bessel beam generating device) of the present invention:

In a conventional Bessel beam generating device using an axicon lens, it was difficult to adjust the focal length. Also, in a Bessel beam generating device that blocks the central portion of the beam, it was necessary to block the central portion where the light intensity is highest, and therefore a significant reduction in light intensity was unavoidable.

In the Bessel beam generating device of the present invention, because it can generate a donut-shaped Bessel beam with almost no reduction in light intensity and with an arbitrary radius and divergence angle, the focal length and depth of focus can be set freely. In this Bessel beam generating device, the attenuation can be compensated by a high light intensity, so the irradiation beam can reach deep positions from the surface of the material to be irradiated.

In the Bessel beam generating device, the lens is configured to irradiate the beams such that the divergence angle of the irradiation beam differs between the circumferential direction and the diameter direction of the circle.

This allows the distance between adjacent optical fibers (i.e., the circle's radius) to be set freely in the Bessel beam generating device, and therefore the degree of freedom in design can be improved.

In the Bessel beam generating device, the fiber tip is arranged tilted inward with respect to the diameter direction of the circle.

This allows the focal length to be determined by the tilt angle of the fiber tips in the Bessel beam generating device, meaning that thereafter only the divergence angle needs to be adjusted. Therefore, the degree of freedom in designing the lens that emits the irradiation beam is improved.

21 In the Bessel beam generating device, each said optical fiber is provided with a voltage applying device (voltage applying unit) for temporally advancing or delaying the wavefront of the emitted light.

This allows the focal position of the disk illumination beam in the Bessel beam generating device to be moved in a direction perpendicular to the optical axis of the disk illumination beam.

22 In the Bessel beam generating device, a movable part (lens driving unit) is provided that can rotate the lens.

This allows the focal position of the disk illumination beam in the Bessel beam generating device to be moved along the optical axis direction of the disk illumination beam.

1 11 a light source (the light source in the light generation unit) that emits a laser beam; 13 a beam splitting unit (beam splitting unit) that generates split beams by splitting a laser beam emitted from a single light source; 15 15 15 a group of optical fibers (optical fiber) comprising at least four optical fibers or more (32 optical fiber) arranged such that their tips (fiber tipA) are on the same circle at equal intervals, each said fiber tip being arranged such that it is tilted at the same angle with respect to the diameter direction of the circle; 14 an entrance portion (entrance portion) that causes the split beams to enter each of the optical fibers; 16 a lens (lens) that adjusts the beam of light emitted from each said optical fiber so that diverging light with a donut-shaped cross-section having a hollow center that travels inward is emitted from the group of optical fibers as a disk illumination beam; 18 a light receiving unit (light receiving unit) that receives a return light beam reflected from the disk illumination beam and converts it into an electrical signal; and 31 an analysis unit (control unit) that calculates the position of a reflection point of the measurement object by analyzing the electrical signal. In the optical scanning device (OCT apparatus) of the present invention:

This allows the focal length and depth of focus to be set large in the optical scanning device, so that deeper positions from the surface can be scanned, and even without moving the focus, the shape or other attributes of the object over a wide range in the optical axis direction can be observed.

110 125 126 In the Bessel beam generating device (disk-shaped Bessel beam generating device) of the present invention: a reflective lens (reflective lens) that reflects an incident laser beam outward from the optical axis; and a reflective cover portion (reflective cover portion) arranged to cover the reflective lens and that reflects the laser beam traveling outward toward the inside are provided.

This allows the laser beam to be expanded once and then reflected inward in the Bessel beam generating device, making it possible to generate a donut-shaped Bessel beam with virtually no reduction in light intensity and with an arbitrary radius and divergence angle, and thus the focal length and depth of focus can be set freely.

Furthermore, by two reflectors, the high-intensity central portion of the laser beam can be moved outward, and the low-intensity outer portion of the laser beam can be moved to the center, thereby inverting the intensity distribution in the beam such that the farther out, the higher the intensity of the light in the donut-shaped Bessel beam. In this Bessel beam, the focal distance is shorter on the inner side and longer on the outer side, so that the light intensity is increased for the outer portions where attenuation is greater, allowing the disk illumination beam to reach far distances despite attenuation.

In the Bessel beam generating device, the reflective lens is configured to reflect the incident laser beam so that the beam travels toward the outside of the optical axis.

This prevents the laser light reflected by the reflective lens from mixing into the return light beam in the Bessel beam generating device, thus minimizing the reduction in light intensity and reducing noise mixed into the return light beam as much as possible.

In the Bessel beam generating device, the reflective lens has a conical shape with an apex angle of 90°.

This allows the laser light to be bent by at least 90° relative to the optical axis of the disk illumination beam in the Bessel beam generating device, preventing the laser light from being reflected back in the return direction of the disk illumination beam's optical axis (the opposite direction of propagation). In addition, having a conical shape ensures that essentially all of the laser light is converted into the disk illumination beam without loss.

111 a light source (the light source in the light generation unit) that emits a laser beam; 125 a reflective lens (reflective lens) on which the laser beam is incident and which reflects the laser beam outward from the optical axis; 126 a reflective cover portion (reflective cover portion) arranged to cover the reflective lens and that reflects the laser beam traveling outward toward the inside; 118 a light receiving unit (light receiving unit) that receives the return light beam reflected from the disk illumination beam and converts it into an electrical signal; and 131 an analysis unit (control unit) that calculates the position of a reflection point of the measurement object by analyzing the electrical signal are provided. In the optical scanning device (OCT apparatus) of the present invention:

This means that the optical scanning device can use a disk illumination beam capable of reaching far distances despite attenuation, so for example, the interior of a blood vessel or deep inside a human body can be scanned, enabling observation of measurement targets that could not be observed with prior OCT devices.

13 14 FIGS.and 210 Next, a third embodiment will be described with reference to. The configuration of the disk-type Bessel beam generating devicediffers from that of the second embodiment described above. In the third embodiment, descriptions of the same components as in the second embodiment are omitted.

13 FIG. 210 230 232 231 235 231 231 233 As shown in, in the disk-type Bessel beam generating device, a laser beam emitted from a micro light sourcehaving directivity in a Cassegrain antenna configuration is reflected by the generatrixof conical sub-reflectorwhose axis is the optical axisof the laser beam. The conical sub-reflectoris configured such that a ring-shaped virtual light source formed around the sub-reflectorby the reflected laser beam (the extended line of the laser traveling toward an elliptical main reflector) is located at the first focus of the ellipse.

233 234 233 234 233 230 231 234 233 After that, the laser beam reflected by the elliptical main reflectoris gathered in a ring shape at the second focusof the ellipse on the elliptical main reflector. A ring-shaped directional light source is formed at the second focuson the major axis of the ellipse, thereby generating a modified Bessel beam. In other words, the elliptical main reflector, the micro light source, and the conical sub-reflectorare configured such that the first focus and second focusof the elliptical main reflectorserve as a virtual light source and a directional light source, respectively.

232 233 Furthermore, by making the generatrixof the conical sub-reflector curved (convex or concave) instead of straight, the position of the virtual light source (i.e. the position of the first focus of the ellipse) can be changed. This increases the degree of freedom in designing the elliptical main reflector, and as a result, the effective range of the Bessel beam can be modified.

14 FIG. 14 FIG. 13 FIG. 210 240 240 Also, as shown in, in a disk-type Bessel beam generating deviceX, if the main reflectoris made not an elliptical surface but a parabolic surface or an aspherical (free-form) surface, the laser light from the main reflectorbecomes parallel rays, slightly diverging rays, or rays with a focal point beyond the effective range of the Bessel beam. In this way, a Bessel beam can be generated that is closer to the Bessel beam produced by an axicon lens. In, components corresponding to those inare denoted with the same reference numerals plus “X”.

210 15 a group of at least four light emitters (32 optical fiber) is arranged at equal intervals on the same circle such that light is emitted from the tip of an optical waveguide portion, with the optical axis of the light emitted from each said light emitter maintained at the same angle with respect to the diameter direction of the circle; 14 an entrance portion (entrance portion) that splits a laser beam emitted from a single light source and causes the split light to enter each of the optical waveguide portions; and 16 an optical waveguide portion (lens) having a function to make the phase and amplitude of the emitted light identical at each said light emitting portion are provided. According to the above configuration, in the modified Bessel beam generating device (disk-shaped Bessel beam generating device) of the present invention:

In the modified Bessel beam generating device, each said light emitter has on its front side an optical axis adjustment lens for adjusting the angle between the optical axis of the emitted light and the diameter direction of the circle.

In the modified Bessel beam generating device, each said optical waveguide portion is provided with a phase/amplitude adjustment device for varying the wavefront of the emitted light spatially or temporally.

In the modified Bessel beam generating device, a rotationally symmetric conical reflector whose generatrix is linear or curved is provided to reflect the incident laser beam outward from the optical axis, and a reflective cover portion is arranged to cover the conical reflector and re-reflects the reflected wave from the conical reflector by means of an elliptical main mirror having the optical axis as its axis of rotational symmetry.

In the modified Bessel beam generating device, the reflective cover portion re-reflects the reflected wave by means of a parabolic main mirror having the optical axis as its axis of rotational symmetry.

In the above embodiments, although not described in detail, by performing frequency modulation on the laser light using an M-sequence code or other PN code (Pseudo Random Noise), it is possible to reduce noise and improve the measurement resolution. Specifically, a coherent continuous light is generated by the light source, and the continuous light is converted into a periodic train of optical pulses with low interference between adjacent pulses. The optical pulse train is phase-modulated with a two-phase modulation using a code having an autocorrelation property (a PN code such as an M-sequence), and one of the split optical pulse trains is frequency shifted. One of the split optical pulse trains is used as an illumination optical system for irradiating the measurement object, and the other split optical pulse train's optical path length is adjusted to be the same as that of the measurement optical system and used as a reference optical system. A photodetector receives the optical pulse train output from the reference optical system and the return light from the measurement optical system. Based on the optical signal received by the photodetector, a difference signal having the shift frequency of the frequency shifter as a beat frequency of the backscattered wave from the measurement object is extracted by a filter. The filter's output and a reference signal synchronized with the frequency shifter's shift frequency are combined and demodulated by a demodulator. The signal output by the demodulator is analyzed by the analysis unit to calculate the positions of reflection points of the measurement object. The detailed configuration is described in WO 2019/017392.

13 15 15 13 14 In the first embodiment described above, the beam splitting unitis composed of an arrayed-waveguide grating or the like, but the present invention is not limited to this. For example, a doughnut-shaped beam may be formed by using an inverse axicon lens having an overall conical concave shape with a bulging slope (i.e., a shape that mates with a narrowing conical shape), and made to enter the ring-arranged optical fiber. In other words, the light beam is split at the stage of being coupled into the optical fiber. In this case, the inverse axicon lens serves the roles of the beam splitting unitand the entrance portion.

110 105 110 In the second embodiment described above, only the disk-shaped Bessel beam generating deviceis attached to the tip of the optical fiber, but the present invention is not limited to this. For example, the light source and the light receiving unit can be attached together with the disk-shaped Bessel beam generating deviceas a tip assembly, and the exchange of electrical signals can be performed between the tip assembly and an external device.

Furthermore, although not specifically mentioned in the above embodiments, devices such as a distance measuring device (e.g., an accelerometer) capable of measuring movement distance, or a position specifying device that can determine the position of the disk-shaped Bessel beam generating device, may be added to the disk-shaped Bessel beam generating device. This enables accurate determination of the position of the disk-shaped Bessel beam generating device and can improve the accuracy of image processing. Even if such devices are not present, by identifying the same positions in image processing or calculating motion vectors, it is possible to composite images when the disk-shaped Bessel beam generating device has scanned.

Also, in the above embodiments, it is possible to configure a single probe by combining and fixing multiple disk-shaped Bessel beam generating devices, or to perform simultaneous imaging from multiple directions by using multiple disk-shaped Bessel beam generating devices. This enables a wider range to be measured in a single measurement and can be expected to further improve accuracy.

In the above embodiments, an optical fiber was used as the optical waveguide portion, but the present invention is not limited to this. For example, the disk-shaped Bessel beam generating device may be implemented as an integrated photonic optical circuit, and various waveguides such as those in silicon photonics can be used as the optical waveguide portion.

The disk-shaped Bessel beam generating device can also be configured such that a laser beam emitted from a micro light source with directivity in a Cassegrain antenna configuration is reflected by a conical sub-reflector (with the optical axis of the laser beam as its axis of symmetry) to create a ring-shaped virtual light source around the sub-reflector, and light from this virtual light source is reflected by a rotating elliptical surface main reflector, so that on the major axis of the ellipse an actual focal point is formed where light is gathered in a ring shape. In this way, a ring-shaped directional light source is formed, and a modified Bessel beam is generated.

Further, in the Bessel beam generating device of the present invention, a laser beam emitted from a micro light source with directivity in a Cassegrain antenna configuration can be incident, the laser beam's optical axis being the axis of symmetry of a conical sub-reflector, such that a ring-shaped virtual light source is formed around the sub-reflector. Light from this virtual light source is reflected by a rotating parabolic surface main reflector to re-reflect the beam, generating a conical wavefront with an apex angle that is nearly an obtuse angle close to 180 degrees. These conical wavefronts are phase-combined on the optical axis to generate a Bessel beam.

Note that the reason for using an elliptical surface as the main reflector is that a ring-shaped circle is formed at the focus of an ellipse. When a ring-shaped circle is formed, the side lobes around the Bessel beam due to the Fresnel zone are reduced.

In the second embodiment, for the inner rays with a large angle, the peripheral portion of the light emitted from the fiber (where the center portion is strong and the periphery is weaker) forms the nearest Bessel beam, and the strong central portion of the light forms a beam at a farther location. This offsets the attenuation of light in human tissue, making it suitable for use in, for example, a catheter that measures inside blood vessels.

The present invention can be used, for example, in an OCT apparatus for medical use to observe inside the body of a human or animal, or for detecting defects such as scratches in paint.

1 101 ,: OCT apparatus 2 102 ,: external device 4 104 ,: measurement unit 10 110 ,: disk-shaped Bessel beam generating device 11 111 ,: light generation unit 12 : collimation unit 13 : beam splitting unit 14 114 ,: entrance portion 15 : optical fiber 15 A: fiber tip 16 : lens 17 : optical branching unit 18 118 ,: light receiving unit 19 31 131 ,,: control unit 21 : voltage applying unit 22 : lens driving unit 23 : external interface 119 : signal processing unit 125 : reflective lens 126 : reflective cover portion 131 : control unit